A phase change memory is a non-volatile memory with high operating speed, simple structure and high reliability. Consequently, the phase change memory is gradually favored by users. Moreover, with increasing development of the semiconductor technologies, a three-dimensional (3D) phase change memory is introduced into the market.
Generally, the material of the phase change memory is in a crystalline state or an amorphous state. In case that the material of the phase change memory is in the crystalline state, the resistance is lower. In case that the material of the phase change memory is in the amorphous state, the resistance is higher. That is, the storage state of the phase change memory is determined according to the resistance of the material of the phase change memory.
FIG. 1A schematically illustrates a memory cell of a conventional 3D phase change memory. FIG. 1B is a schematic perspective view of the conventional 3D phase change memory. FIG. 1C is a schematic circuit diagram illustrating an equivalent circuit of the conventional 3D phase change memory.
As shown in FIG. 1A, the memory cell 110 comprises a storage element 102 and a selector 104. The storage element 102 is a phase change element. Moreover, the storage element 102 can be considered as a resistor with variable resistance. The storage element 102 is programmed to have high resistance or low resistance. The high resistance and the low resistance indicate different storage states. The selector 104 is a diode. Moreover, the storage element 102 and the selector 104 are connected with each other in series.
As shown in FIG. 1B, the phase change memory 100 comprises plural word lines WL0˜WL5, plural bit lines BL0˜BL5 and plural memory cells. The bit lines BL0˜BL5 are metal lines along a first direction. The word lines WL0˜WL5 are metal lines along a second direction. The first direction and the second direction are perpendicular to each other. Moreover, each memory cell is connected between the corresponding word line and the corresponding bit line.
For example, the memory cells c0˜cb are connected between the word lines WL0˜WL5 and the bit lines BL0, BL2 and BL4. Please refer to FIG. 1C. The memory cell c0 is connected between the bit line BL0 and the word line WL2. The memory cell c1 is connected between the bit line BL0 and the word line WL1. The memory cell c2 is connected between the bit line BL0 and the word line WL0. The memory cell c3 is connected between the bit line BL2 and the word line WL2. The memory cell c4 is connected between the bit line BL2 and the word line WL1. The memory cell c5 is connected between the bit line BL2 and the word line WL0.
Similarly, the memory cell c6 is connected between the bit line BL2 and the word line WL5. The memory cell c7 is connected between the bit line BL2 and the word line WL4. The memory cell c8 is connected between the bit line BL2 and the word line WL3. The memory cell c9 is connected between the bit line BL4 and the word line WL5. The memory cell ca is connected between the bit line BL4 and the word line WL4. The memory cell cb is connected between the bit line BL4 and the word line WL3.
By controlling the voltages of the bit lines BL0˜BL5 and the word lines WL0˜WL5, the corresponding memory cell is programmed or read.
The structure of the phase change memory 100 can be further applied to a resistive memory. For increasing the production yield and the reliability of the memory, it is important to search for the better materials of the storage element and the selector.
FIG. 2 is a schematic circuit diagram of a memory cell of the phase change memory. The memory cell is disclosed in Advanced Materials 2016, 28, 356-362, and the contents of which are hereby incorporated by reference. As shown in FIG. 2, the memory cell 210 comprises a storage element 202 and a selector 204. The storage element 202 and the selector 204 are connected with each other in series. The storage element 202 comprises a platinum (Pt) metal layer, a tantalum (Ta) metal layer, and a tantalum oxide (TaOx) between the platinum (Pt) metal layer and the tantalum (Ta) metal layer. The selector 204 comprises two platinum (Pt) metal layers, two tantalum nitride (TaN1+x) layers between the two platinum (Pt) metal layers, and a tantalum oxide (Ta2O5) layer between the two tantalum nitride (TaN1+x) layers.
Moreover, by setting or resetting the storage element 202, the resistance of the storage element 202 is adjustable. Moreover, the selector 204 has the characteristics of a diode.
From the above discussions, the memory cell of the conventional phase change memory is composed of two electronic components that are connected with each other in series.